Solid bulk cargo – Any material, other than liquid or gas, consisting of a combination of
particles, granules or any larger pieces of material, generally uniform in composition, and
loaded directly into the cargo spaces without any intermediate form of containment.

Bulk carrier, bulker – A vessel designed to carry dry cargo, loaded into the vessel with no
containment other than that of the ship,s boundaries, as distinguished from the liquid
bulk carrier or tanker. Conventional bulk carrier is constructed with a single deck, single
skin, double bottom, hopper side tanks and topside tanks in cargo spaces.

Bulk carriers are designed to load a maximum deadweight of any type of bulk cargo from heavy ore to light grain . The loading, carriage and finally the discharge of dry bulk
cargo is not as simple or straight forward as most people
would imagine.

Fig: Gearless bulk carrier

Many bulk cargoes have hazardous
properties, or can change their properties on passage.
The ship can be easily damaged by incorrect loading e.g.
loading a forward hold to it maximum can cause the ship
to bend. This ‘stress’ can have life threatening results at
sea in rough weather.

Residues from previous cargoes
can also seriously effect latter cargoes. Water damage can
also have devastating effect on some bulk cargoes e.g.
cement power. It is not easy to verify true weights or
quantities of cargoes loaded or discharged. All these
factors have a serious consequence on the methods of
operation for the safe carriage of bulk cargoes.
Discharging bulk cargo using
“grab”

Bulk cargoes have an inherent tendency to form a
cone when they are loaded if conveyor belts or similar
systems are not supervised and controlled. The angle
formed by this cone is known as the `angle of repose'
and varies with each cargo. Cargoes such as iron ore
will form a steep angled cone, whereas cargoes that
flow freely form a shallow angled cone. A cargo with a
low angle of repose has the potential to shift during
passage.

For some cargoes, bulldozers may
be required to spread the load into
the sides of the holds as cargo is
nearing completion.

Most dry-bulk carriers depend on
shoreside facilities for cargo loading and discharge, but some bulk carriers have self-unloading
features with conveyors below the cargo holds, or with cranes on deck.
Outlined below some of the more common bulk cargoes and their properties:

Coal

Coal is transported on all types of bulk carriers from handy size to VLCBs.
However, it is not an easy or straight forward cargo to handle. It can emit methane
gas and it is self-heating. In addition coal contains sulphur which causes severe
corrosion when in contact with the ship's steelwork.

In most ports the cargo is loaded
wet to reduce dust. Much of this moisture settles on passage and is pumped out
through the ship's hold bilges which means that less weight is discharged than is
loaded.

This cargo is loaded very fast, 10,000 tonnes an hour is not unusual. The
loading and de-ballasting of the ship must be meticulously planned to ensure that the
vessel is not overstressed. There is very little chance of damaging the cargo but the
ship can receive extensive damage during the discharge operation from the equipment
used.

Many different types of concentrates are handled in various
parts of the world and in varying quantities. Most of these cargoes are extremely
heavy and have a low transportable moisture limit (TML). This means that if the
moisture content of the cargo become greater than the TML the cargo can liquefy and
turn into a slurry. When this happens on board, the cargo moves from side to side as
the ship rolls which reduces the ship's righting lever. It does not require much cargo
weight to capsize the vessel when this happens, it a loss of stability due to free surface
effect. Some of the most dangerous cargoes where this can happen are copper, lead or
zinc concentrates, magnetite, limonite and most pyrites.

Grain

One of the most difficult and dangerous cargoes
to carry in bulk are grain cargoes. Most grains have an
angle of repose (slip angle) of about 20° from the
horizontal, which means that if the ship rolls more than
20° the cargo will shift. Then this happens the ship will
develop a large list, lying on her side and still rolling will
obviously cause a greater shift of cargo which in turn will
capsize the vessel.

Most authorities therefore request that
the master proves that his ship is capable of remaining
stable even if the grain cargo shifts. This is done by the
compiling of the Grain Loading Form which fully
outlines the ships stability at the worse condition on passage.

Naturally grain cargoes, like any foodstuff, are susceptible
to claims with contamination from a previous cargo and in addition can easily be
damaged by water.

Vermin can also be a problem. Cargo holds must be clean and dry prior to the loading
of any grain cargo and most grain charters demand a survey of the ship's hold prior to
loading for this reason.

Obviously any moisture is going to ruin a cargo of cement but probably a
greater danger to the vessel is the dust that can be produced during the loading and
discharge of the cargo. If it is not removed promptly or gets into the ship's air intakes
it can cause some long term problems to the vessel.

Salt- Salt, strangely enough, is not damaged from water, in fact the cargo can be
loaded slightly moist. However, it can get rust stained from the ship's steelwork,
therefore the ship must cover all the steel within the cargo hold with a lime wash
solution thereby keeping the salt off the steelwork.

Again a supposedly harmless cargo that does have some hidden
dangers. Some shipments many be subject to oxidation leading to depletion of oxygen
and an increase of carbon dioxide in the cargo hold and adjacent spaces.

Fig: Bulk terminal woodchip loading

In addition,
woodchips can be easily ignited by external sources, it is readily combustible and can
also ignite by friction. The stowage factor can vary greatly with this cargo depending
on the wood type, the moisture content and the type of loading head used. Even
different loading operators can achieve varying stowage factors with the same cargo.